Energy and the First Law of Thermodynamics

Energy (E)

Extensive property of a system, includes various forms.

Kinetic Energy (KE)

Energy due to motion, calculated as 1/2 mv².

Potential Energy (PE)

Gravitational energy, calculated as mgh.

Internal Energy (U)

Energy from molecular motion and chemical bonds.

Energy Change (ΔE)

Difference in energy, ΔE = ΔU + ΔPE + ΔKE.

Work (W)

Energy transfer that could raise a weight.

Work Equation

W = ∫ F·ds, includes mechanical and electrical work.

Work Units

Measured in Joules (J), N·m, or ft·lbf.

Path Function

Depends on process path, unlike state functions.

Inexact Differential

Represents work (W) and heat (Q) changes.

Polytropic Process

Describes relationship between pressure and volume.

Heat (Q)

Energy transfer due to temperature difference.

Heat Units

Same as work, measured in Joules (J).

Power (Ẇ)

Rate of energy transfer by work, Ẇ = F·V.

Heat Transfer Rate (Q̇)

Rate of energy transfer by heat, Q̇ = dQ/dt.

Conduction

Heat transfer through direct contact.

Convection

Heat transfer between solid and moving fluids.

Radiation

Heat transfer via electromagnetic waves.

Heat Flux (q̇)

Heat transfer rate per unit area.

Specific Energy (e)

Energy per unit mass, e = E/m.

Specific Internal Energy (u)

Internal energy per unit mass, u = U/m.

1st Law of Thermodynamics

Energy conservation principle for closed systems.

Energy Balance Equation

ΔE = Q - W, relates heat and work.

Rate Form of Energy Balance

dE/dt = Q̇ - Ẇ, for dynamic systems.

Sign Convention for Q

Positive Q for heat added to system.

Sign Convention for W

Positive W for work done by system.